The purpose of the Aging Animal and Longevity Assessment Core is to provide Center investigators and researchers in aging outside the University with a broad spectrum of uniformly maintained, specific-pathogen free rodent models for the study of aging, according to their needs. The Core will continue to play a central role in the Nathan Shock Aging Center. All animals in the Core will be supported by NIA or other aging grants. The Core will breed, maintain and monitor aging rodent colonies, determine their longevity and age-related changes in weight, body composition and food intake, and distribute these animals to Center members and others for basic research on aging. In addition, the Core will maintain for pilot studies small populations of two murine models that Center investigators have recently found to have exceptional potential for understanding fundamental mechanisms of aging: 1) rapamycin-treated genetically heterogeneous mice and 2) two groups of recombinant inbred mouse strains at the extremes of the distribution of strain responses to calorie restriction (CR) one group of strains that shows characteristic life extension in response to CR and the other group of strains that responds with life shortening. These and other advances enabled by this Core underscore its importance as a generator of biogerontologic discovery. The Specific Aims of the Core are as follows: 1 To breed and maintain new and established rodent models for study of the mechanism of aging and/or age-related disease processes. To conduct lifespan studies of genetically, nutritionally, or pharmacologically manipulated models according to the requirements of investigators funded by the NIA and other granting sources. To provide animal models of exceptional biogerontological interest for baseline pilot studies. To provide diets containing rapamycin and other drugs to the biogerontological community at large. To educate and advise faculty, fellows, and students interested in aging on the special requirements of animal husbandry in aging research.